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19 April 2024 |
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Simultaneous ASCA And RXTE Observations of Cygnus X--1 During Its 1996 State Transition | | Wei Cui
; K. Ebisawa
; T. Dotani
; A. Kubota
; | | Date: |
14 Nov 1997 | | Subject: | astro-ph | | Affiliation: | MIT), K. Ebisawa (GSFC/USRA), T. Dotani (ISAS), and A. Kubota (Univ. of Tokyo | | Abstract: | We report results from simultaneous ASCA and RXTE observations of Cyg X-1 when the source made a rare transition from the hard (= low) state to the soft (= high) state in 1996. These observations together cover a broad energy range ~0.7--50 keV with a moderate energy resolution at the iron K-band, thus make it possible to disentangle various spectral components. The low-energy spectrum is dominated by an ultra-soft component, which is likely to be the emission from the hottest inner portion of the accretion disk around the black hole. At high energies, the X-ray spectrum can be described by a Comptonized spectrum with a reflection component. The Compton corona, which upscatters soft ``seed photons’’ to produce the hard X-ray emission, is found to have a y-parameter ~0.28. The hard X-ray emission illuminates the accretion disk and the re-emitted photons produce the observed ``reflection bump’’. We show that the reflecting medium subtends only a small solid angle ($sim 0.15 imes 2pi$), but has a large ionization parameter such that iron is ionized up to ion{Fe}{24}-ion{Fe}{26}. The presence of a broad iron line at $6.58pm0.04$ keV is also consistent with a highly ionized disk, if we take into account the gravitational and Doppler shift of the line energy. These results imply a geometry with a central corona surrounding the black hole and the reflection occurring in the innermost region of the disk where matter is highly ionized. | | Source: | arXiv, astro-ph/9711164 | | Services: | Forum | Review | PDF | Favorites | |
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